Molybdenum oxide containing high permeability zinc-manganese ferrite



April 27, 1965 A. PIERROT ETAL 3,180,833

MOLYBDENUM' OXIDE CONTAINING HIGH PERMEABILITY ZINC-MANGANESE FERRITEOriginal Filed Feb. 5, 1959 O I OJOI 0.20 0.50 0.75 1-0 0.05 0.15 0.25CYRSTALL/ZAT/ON AGE NT INVENTORS.

ANDRE P/E'IQRO T y Y VES SCROEL ATTORNEY United States PatentOfiice3,ld0,833 Patented Apr. 27, 1965 This is a division of applicationSerial No. 791,405, filed February 5, 1959, now Patent No. 3,057,802,granted October 2, 1962.

The present invention relates to ferromagnetic mate rials of the ferritetype, for use in the art of telecommunications, electronics andelectrotechnics for transformer cores, inductance coils and any otherapplication for which it is necessary to have a soft magnetic materialwith high permeability and low losses.

The definitions of the coefiicients employed to characterize themagnetic materials obtained in accordance with the invention are givenin the following:

The permeability ,u indicated is the permeability measured for a fieldof 2 millioersteds, i.e. the initial permeability for a frequency of 800c./s. at the temperature of 20 C. 1

The coefficients of losses employed are the coefficients defined for afrequency of 800 c./s., a field of l ampereturn per centimetre, and aninductance of 1 henry at the temperature of 20 C., in accordance withthe relation:

f 2 N .I f f 1 800 In... 800 L+t 800 L (1) in which:

R is the resistance of losses in alternating current in the magneticcore of an inductance coil, in ohms;

L is the inductance of said coil in henrys;

is the frequency, in cycles per second;

N is the number of turns of the winding of the coil;

I is the elfective value of the current t me Winding,

in amperes;

l is the length of the mean magnetic line of force,

in cm.

The coefficients of eddy current losses F,,, of hysteresis h and oftrainage t relating to a continuous magnetic circuit, have been measuredunder the following conditions:

The coefficient of eddy current losses P is expressed in ohms per henry,for the frequency 800 c./s., measured for a field of 2 millioersteds andat a temperature of about 20 C., for magnetic circuits of which thecrosssection is about 0.3 cm. (0.5 x 0.6 can);

The coefficient of hysteresis losses h, expressed in ohms per henry, fora field of l =1 at ./cm.

and for the frequency f=800 c./s., is measuredbetween fields of 2 and 22millioersteds, at the frequency 800 c./s. and at the temperature ofapproximately 20 C.;

The coefiicient of trainage losses t, expressed in ohms per hen-ry andfor the frequency f=800 c./s., is deduced from the ordinate at theorigin of the curves for a zero field,- at a temperature of about 20 C.According to (l), in effect, for i=0 and 1:0, we have;

hence we deduce t.

The coefficient F,,, It and t indicated relate to continuous circuitswithout airgap and are of particular interest for transformers withoutairgap.

The coefiicients 10 10 and 10 have been introduced, which make itpossible to judge the quality of the various materials, and do notdepend on the airgap, if any.

It is, moreover, well known that it is desirable in telecommunication toproduce, in as small as possible a volume, transformers With as large aspossible a passb-and, and having a very low attenuation in that band.This necessitates the use of materials with high initial permeabilityand low losses.

One particular object of the invention is to obtain magnetic materialsfulfilling these conditions.

In accordance with the present invention, magnetic materials of theferrite type are provided, particularly ferrites of manganese-zinc,characterized by the addition to the basic composition of acrystallizing agent of which the content is between 0.02 and 2% of theweight of the mixture, which causes the material to have an initialpermeability higher than 3000 and which might reach 6000.

In particular, the basic ferrites of manganese-zinc to which theinvention relates are ferrites of which the composition comprises amolecular proportion of ferric oxide Fe O substantially equal to acontent by weight of Fe() comprised between 0 and 5%, and molecularproportions of manganese oxide MnO and zinc oxide Z110 respectivelycomprised between 25 and 30% and between 15 and 25%, as described andclaimed in British specification 730,703. It has moreover been foundthat v for these materials, for best results, the diameter of the grainsmust be as uniform as possible and comprised between 10 and 30 microns.

Molybdenum oxide (M00 is used as a crystallizing agent which makes itpossible to obtain a very homogeneous granular structure with largegrains. Its action is particularly to reduce the temperature ofpreparation of the ferrite.

Owing to the fact that, in the starting mixture used in preparing theferrite, the crystallizing agent is introduced into the mixture ofoxides, the contents indicated are related to the total mass of thecomponents of the starting mixture, in which iron is considered in theform of Fe O and the other constituents in the form of MeO, Merepresenting the bivalent metal or metals.

In order to obtain the permeability claimed, it is very important to usevery pure starting raw materials. As is said in the Britishspecification above referred to, the most harmful impurities are bariumand strontium.

The invention will be better understood with reference to the drawingand to the following example.

The figure represents variations of the ratio ,u /u as a function of thepercentage of molybdenum oxide added,

,u being the initial permeability without the additive and #2 being theinitial permeability with the additive, for a starting composition:

and for annealing for four hours at l,240 C. in pure MIIO 28.3

and

ZIIO 19.2

for the example, the treatment is the same as that indicated in thefollowing for the material Without crystallization agent. Thecrystallization agent is added to the starting mixture before grinding.

The oxides in the proportions indicated above are ground for from 24 to28 hours in a steel mill with steel balls, the water added being equalin litres to about 1.5 times the weight of the material in hilogrammes.

The material, after being filtered and dried, is compressed into coresat a pressure of about 1 to 10 tons per CHLZ, for example tons per cm.

The cores passed into the stove at 200 C. for evaporation of the organicbinding agent possibly employed during compression, are annealed in anitrogen atmosphere containing about 1% oxygen. The temperature is 1,240C., the duration four hours and the cooling is carried out for about 15hours in pure nitrogen. The cooling of the annealed substance isextremely important, because it is during this cooling that the excessof trivalent ions of Fe O is transformed into bivalent ions, leading toa material containing as many molecules of trivalent ions as moleculesof bivalent ions and having very good magnetic properties.

The material obtained in this way has the following characteristics:

h 0 -10 -200 -10 =5, and u Curie point 0 z170 C.

4 Example For a product having the starting composition previouslyindicated, and to which has been added 0.20% by weight of molybdenumoxide M00 and treated in the manner described, the magnetic propertiesare as follows:

While the principles of the invention have been described above inconnection with specific embodiments, and particular modificationsthereof, it i to be clearly understood that this description is madeonly by way of example and not as a limitation on the scope of theinvention.

What is claimed is:

A body of ferromagnetic ceramic material of high permeability which isthe reaction product obtained by heating for a period of two to fourhours at a sintering temperature above 1170 C. up to 1280 C. in anatmosphere essentially constituted by an inert gas containing between0.01 and 1.2% of oxygen, followed by cooling for a period of at leastten hours in an inert atmosphere, a mixture of ferric oxide, an oxide ofmanganese and zinc oxide the starting mixture of oxides and the heattreatment yielding a final material containing between 49.7 and 50.6mol. percent of ferric oxide, between 0.3 and 7.5 mol. percent offerrous oxide, between 25 and 30 mol. percent of manganous oxide and theremainder zinc oxide and in which there is added to the starting mixtureof oxides between 0.07 and 0.30% by weight of the molybdenum oxide.

References Cited by the Examiner UNITED STATES PATENTS 2,736,708 2/ 56Crowley 25262.5 3,009,880 11/ 61 Lessotf 25262.5

FOREIGN PATENTS 730,703 5/55 Great Britain.

1,125,577 7/56 France.

MAURICE A. BRINDISI, Primary Examiner.

